It has been proposed in U.S. Pat. No. 5,244,861 to utilize biaxially oriented polypropylene laminated to cellulose photographic grade paper for use as a reflective receiver for thermal dye transfer imaging processes. In this invention low density polyethylene is melt extrusion coated onto the backside of the reflective receiver to balance the reflective receiver for curl, provide waterproofing to the paper, and provide the proper backside roughness for printer transport.
In the formation of photographic papers, where a light sensitive emulsion layer containing gelatin is coated onto the base paper that has been extrusion coated with low density polyethylene resin, there is a need to provide a base paper with improved resistance to curl. When the relative humidity is greater than 50% or less than 20%, as is common in the storage of photographic images, the curl of photographic paper interferes with the viewing of images. A solution to the photographic curl problem has been proposed in U.S. application 08/864,228 filed May 23, 1997. In that invention, a mechanism to reduce curl in relative humidity greater than 50% or less than 20% is accomplished by applying a biaxially oriented polymer sheet to the backside of the paper base to balance the forces caused by the expansion and contraction of the emulsion layer in a relative humidity environment greater than 50% or less than 20%.
During photofinishing of traditional photographic papers, traditional polyethylene coated silver halide photographic paper is chopped in the cross direction as slit rolls of photographic paper are printed with consumer images. Since there is no worldwide photofinishing standard for chopping mechanisms, there exists many different types of chopping mechanisms that are used in photofinishing equipment around the world to chop rolls of slit photographic paper into consumer images. The chopping mechanisms differ in chopping rate, knife geometry, and force applied to the chopping knife. While the invention proposed in U.S. application 08/864,228 filed May 23, 1997, now U.S. Pat. No. 5,902,720, does significantly reduce image curl, it has been found that the biaxially oriented polymer sheet on the bottom side can interact with some chopping mechanisms, such as the slow speed rotary knife in the Gretag 750 Masterlab printer, and as a result leave undesirable fibrous projections along the chopped edge which significantly reduce the commercial value of the image. It would be desirable if a bottom side biaxially oriented sheet could be formed with the desired strength properties to control image curl and improved to provide efficient chopping in the cross direction.
During photofinishing, traditional polyethylene coated silver halide photographic paper is punched with an index hole which is used as a chopping locator during the finishing operation as slit rolls of photographic paper are printed with consumer images. Since there is no worldwide photofinishing standard for punching mechanisms, there exists many different types of punching mechanisms that are used in photofinishing equipment around the world. The punching mechanisms differ in punch geometry, punch force, and punching rate. While it has been found that the lamination of a biaxially oriented sheet to the bottom side does significantly improve image curl, the additional strength added to the imaging support with the biaxially oriented polymer sheet does increase the force to complete a successful punch. An inaccurate or incomplete punched hole will lead to undesirable results in the photofinishing operation as the photofinishing equipment will not image in the proper location and jams can occur which significantly reduce the efficiency of the photofinishing operation. It would be desirable if a bottom side film could be improved to aid in efficient photofinishing punching.
In the formation of reflective receivers for digital imaging systems such as Ink Jet and Thermal Dye Transfer, there is also need to reduce the curl of the image. Lamination of a high strength biaxially oriented polyolefin sheet to the backside of the image does improve the curl over the common practice of melt extrusion coating a layer of polyolefin. Reflective receivers for digital imaging systems that have biaxially oriented sheets to control curl can be difficult to convert from wide roll format into imaging sheet formats. Converting difficulties resulting from a high strength bottom biaxially oriented polymer sheet could result in fibrous projections on the cut sheet that can reduce the commercial value of the reflective receiver. For Ink Jet and Thermal Dye Transfer receivers it would be desirable if a bottom biaxially oriented polymer sheet could be formed with the strength properties to control curl and provide improved cross direction cutting for efficient slitting of the receiver in manufacturing.